U.S. patent number 4,303,756 [Application Number 06/207,422] was granted by the patent office on 1981-12-01 for process for producing expandable thermoplastic resin beads.
This patent grant is currently assigned to Sekisui Kaseihin Kogyo Kabushiki Kaisha. Invention is credited to Mutsuhiko Kajimura, Hideaki Sasaki.
United States Patent |
4,303,756 |
Kajimura , et al. |
December 1, 1981 |
Process for producing expandable thermoplastic resin beads
Abstract
A process for producing expandable thermoplastic resin beads
which comprises suspending in an aqueous medium 20 to 70% by weight
of a random copolymer of propylene and ethylene containing 1 to 10%
by weight of ethylene and 99 to 90% by weight of propylene and 30
to 80% by weight of a vinyl aromatic monomer such as styrene,
polymerizing the vinyl aromatic monomer in the presence of a
polymerization catalyst to graft the vinyl aromatic monomer onto
the backbone of the random copolymer and, optionally, adding a
cross-linking agent, to form graft-copolymerized thermoplastic
resin beads, and introducing a blowing agent into the thermoplastic
resin beads. The resulting resin beads have excellent foamability
and molding fusability, and a foamed shaped article having superior
thermal stability can be prepared from these beads.
Inventors: |
Kajimura; Mutsuhiko (Moriyama,
JP), Sasaki; Hideaki (Kusatsu, JP) |
Assignee: |
Sekisui Kaseihin Kogyo Kabushiki
Kaisha (Nara, JP)
|
Family
ID: |
26902228 |
Appl.
No.: |
06/207,422 |
Filed: |
November 17, 1980 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
951879 |
Oct 16, 1978 |
|
|
|
|
Current U.S.
Class: |
521/59; 521/139;
521/140; 521/60; 525/193; 525/288; 525/292; 525/302; 525/316;
525/317; 525/322 |
Current CPC
Class: |
C08F
255/04 (20130101); C08J 9/18 (20130101); C08F
255/04 (20130101); C08F 212/04 (20130101); C08J
2351/06 (20130101) |
Current International
Class: |
C08J
9/00 (20060101); C08J 9/18 (20060101); C08F
255/04 (20060101); C08F 255/00 (20060101); C08J
009/16 (); C08J 009/18 () |
Field of
Search: |
;521/59,60,139,140 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Foelak; Morton
Attorney, Agent or Firm: Armstrong, Nikaido, Marmelstein
& Kubovcik
Parent Case Text
This is a continuation of application Ser. No. 951,879, filed Oct.
16, 1978, now abandoned.
Claims
What is claimed is:
1. A process for producing expandable thermoplastic resin beads
which comprises suspending in an aqueous medium graft copolymer
beads containing from 20 to 70% by weight of a random copolymer of
propylene and ethylene containing 1 to 10% by weight of ethylene
and 99 to 90% by weight of propylene and 30 to 80% by weight of a
vinyl aromatic monomer, and introducing a blowing agent composed of
an easily volatilizable hydrocarbon or halogenated hydrocarbon into
the thermoplastic resin beads.
2. The process of claim 1, wherein the amount of random copolymer
in the graft copolymer is 50 to 30% by weight, and the amount of
the vinyl aromatic monomer is 50 to 70% by weight.
3. The process of claim 1, wherein the vinyl aromatic monomer is at
least one monomer selected from the group consisting of styrene,
.alpha.-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene,
vinyltoluene, vinylxylene and isopropylxylene, or a mixture of at
least 50% by weight of at least one of said monomers with another
monomer copolymerizable therewith.
4. The process of claim 1, wherein the blowing agent is introduced
into the resin beads under pressure while in the aqueous
suspension.
5. The process of claim 1, wherein the blowing agent is introduced
into the resin beads by dipping the beads into a liquid organic
blowing agent.
6. The process of claim 1, wherein the random copolymer of
propylene and ethylene is admixed with at least one other polymer
selected from the group consisting of polyethylene, ethylene/vinyl
acetate copolymer, ethylene/vinyl chloride copolymer,
styrene/propylene rubber, polyisobutylene, butyl rubber,
styrene/butadiene rubber, polybutadiene and polybutene, prior to
polymerization with the vinyl aromatic monomer to prepare the graft
copolymer beads.
7. A process for producing expandable thermoplastic graft
copolymerized resin beads which consists essentially of suspending
in an aqueous medium from 20 to 70% by weight of a random copolymer
of propylene and ethylene containing 1 to 10% by weight of ethylene
and 99 to 90% by weight propylene and 30 to 80% by weight of a
vinyl aromatic monomer; adding a polymerization catalyst and
polymerizing the vinyl aromatic monomer to form graft copolymerized
thermoplastic resin beads and subsequently impregnating the graft
copolymerized thermoplastic resin beads with an easily
volatilizable hydrocarbon or halogenated hydrocarbon blowing
agent.
8. In a process for producing expandable thermoplastic graft
copolymerized resin beads which consists essentially of suspending
in an aqueous medium containing 0.01 to 5% by weight, based on
water present in the aqueous medium, of a dispersing agent selected
from the group consisting of polyvinyl alcohol, methyl cellulose,
calcium phosphate, magnesium pyrophosphate and calcium carbonate,
from 20 to 70% by weight of a random copolymer of propylene and
ethylene containing 1 to 10% by weight of ethylene and 99 to 90% by
weight propylene and 30 to 80% by weight of a vinyl aromatic
monomer; adding a polymerization catalyst and polymerizing the
vinyl aromatic monomer to form graft copolymerized thermoplastic
resin beads and subsequently impregnating the graft copolymerized
thermoplastic resin beads with an easily volatilizable hydrocarbon
or halogenated hydrocarbon blowing agent, the improvement
comprising heating the aqueous medium to a temperature at which the
vinyl aromatic monomer can be polymerized before adding the vinyl
aromatic monomer and the polymerization catalyst thereto, and
adding said vinyl aromatic monomer and said polymerization catalyst
to the heated aqueous medium.
9. The process of claim 8, wherein the polymerization is carried
out in the further presence of a crosslinking agent.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing expandable
thermoplastic resin beads, especially those which have superior
foamability and molding fusability and the resulting foamed
articles made from such beads provide good thermal stability.
2. Description of the Prior Art
Generally, it is easy to obtain polystyrene beads having a high
expansion ratio. The resulting foamed articles made from such beads
have high rigidity and good shape retention, but have the
disadvantage in that they are fragile and have poor chemical
resistance, oil resistance and thermal stability. Foamed products
of polypropylene resin, on the other hand, have better elasticity,
chemical resistance, oil resistance and thermal stability than
polystyrene foams. A blowing agent impregnated in polypropylene
resin beads tends to dissipate rapidly, and it is necessary,
therefore, to pre-foam them rapidly after preparation to obtain
expandable beads, or to store these expandable resin beads in a
container under pressure. Accordingly, such impregnated
polypropylene resin beads have disadvantages during storage and
transportation and it is generally difficult to obtain
polypropylene expandable beads having a high expansion ratio.
When polypropylene and polystyrene are simply mixed in an attempt
to obtain a resin having the desirable characteristics of both
polymers, a uniform mixture cannot be obtained. A foamed product
prepared from such a mixture undergoes phase separation, and does
not have an attractive appearance. Many investigations have been
undertaken to remedy this disadvantage. For example, Japanese
Patent Publication No. 36097/72 discloses a process for producing
foamable pellets of a vinyl aromatic polymer which comprises
heat-melting a vinyl aromatic polymer (polystyrene) containing 1 to
15% by weight, based on the total amount of the resin, of a
polyolefin, pelletizing the melt, and impregnating the pellets with
a blowing agent. According to this method, the amount of the
polyolefin mixed is small, and since the vinyl aromatic polymer is
simply physically mixed with the polyolefin, the two resins are not
uniformly mixed and phase separation occurs. As a result, the
impregnation of the blowing agent and the expansion ratio become
non-uniform, and a uniform foamed article cannot be obtained.
Moreover, because of the low polyolefin content, of pliability and
elasticity of the resulting foamed product cannot be improved.
Japanese Patent Publication No. 32623/70 discloses a process for
producing a foamable granular thermoplastic polymer which comprises
dispersing in an aqueous medium a granular thermoplastic resin
composed mainly of an aliphatic olefin resin, a polymerizable vinyl
monomer capable of dissolving or swelling the thermoplastic resin,
a polymerization catalyst and a cross-linking agent composed of an
organic peroxide, introducing a blowing agent which is normally
gaseous or liquid into the aqueous dispersion, and heating the
mixture to a temperature at which the vinyl monomer has a
solubilizing power for the aliphatic olefin resin and the heat also
causes decomposition of the cross-linking agent, whereby the
polymerization of the vinyl monomer, the impregnation of the
blowing agent, and the cross-linking reaction occurs simultaneously
under pressure. Since the polymerization of the vinyl monomer, the
impregnation of the blowing agent and the cross-linking reaction
are performed simultaneously under pressure in this process, a
special manufacturing apparatus is required, and the process has
disadvantages for commercial mass production. In specific
embodiments of this process, the content of polyolefin is very
high, and, therefore, the resulting foamable pellets do not have a
sufficient gas retaining property. Moreover, the resulting foamed
product has the same properties as a foamed article of polyolefin
alone.
SUMMARY OF THE INVENTION
The present inventors made investigations in order to obtain foamed
resins having good properties due to the use of polypropylene such
as superior chemical resistance and thermal stability, good
expansion characteristics, and good cushioning properties. These
investigations led to the discovery that expandable thermoplastic
resin particles of good quality can be obtained by graft
polymerizing a vinyl aromatic monomer in the presence of a
polymerization catalyst onto a backbone of a random copolymer of
propylene and ethylene as a nucleus, and impregnating the resulting
thermoplastic resin beads with a blowing agent.
According to one aspect of this invention, there is provided a
process for producing thermoplastic resin beads which comprises
suspending in an aqueous medium 20 to 70% by weight of a random
copolymer of propylene and ethylene containing 1 to 10% by weight
of ethylene and 99 to 90% by weight propylene and 30 to 80% by
weight of a vinyl aromatic monomer, adding a polymerization
catalyst and graft polymerizing the vinyl aromatic monomer onto the
backbone of the random copolymer to form graft-copolymerized
thermoplastic resin beads.
According to another aspect of the invention, there is provided a
process for producing expandable thermoplastic resin beads, which
comprises introducing a blowing agent composed of an easily
volatilizable hydrocarbon or halogenated hydrocarbon into the
aforesaid thermoplastic resin beads.
DETAILED DESCRIPTION OF THE INVENTION
In the process of this invention, the random copolymer of propylene
and ethylene containing 1 to 10% by weight of ethylene and 99 to
90% by weight propylene is used as a nucleus into which the vinyl
aromatic monomer is absorbed and the vinyl aromatic monomer is
polymerized in the presence of a polymerization catalyst. The
random copolymer itself may include in admixture of at least one of
polyethylene, an ethylene/vinyl acetate copolymer, an
ethylene/vinyl chloride copolymer, a styrene/propylene rubber,
polyisobutylene, butyl rubber, styrene/butadiene rubber,
polybutene, polybutadiene, etc., prior to polymerization with the
vinyl aromatic monomer. Mixing of such a polymer, for example,
serves to increase impact strength at low temperatures and gives
rise to other advantages.
In order to cause rapid absorption of the vinyl aromatic monomer,
the random copolymer is used in a particulate form. It is
preferably in the form of spheres, flattened particles or pellets
having a diameter of about 0.5 to 10 mm.
Examples of vinyl aromatic monomers used in the process of this
invention are styrene, .alpha.-methylstyrene, ethylstyrene,
chlorostyrene, bromostyrene, vinyltoluene, vinylxylene, and
isopropylxylene. These monomers may be used either alone or in
admixture. A mixture of at least 50% of the vinyl aromatic monomer
and a monomer copolymerizable with it, such as acrylonitrile,
methyl methacrylate or methyl acrylate can also be used.
The polymerization catalysts used in the process of this invention
include, for example, organic peroxides such as benzoyl peroxide,
tertiary butyl perbenzoate, lauroyl peroxide, tertiary butyl
peroxy-2-ethylhexanate and tertiary butyl peroxide, and azo
compounds such as azobisisobutyronitrile and
azobisdimethylvaleronitrile.
In the process of this invention, a cross-linking agent is not
always necessary, but may be added. Examples of such cross-linking
agents are di-t-butyl peroxide, t-butyl cumyl peroxide, dicumyl
peroxide, .alpha.,.alpha.-bis(t-butyl
peroxy)-p-di-isopropylbenzene, 2,5-dimethyl-2,5-di(t-butyl
peroxy)hexyne-3,2,5-dimethyl-2,5-di(benzoyl peroxy)hexane, and
t-butyl peroxy isopropyl carbonate. The cross-linking agent is used
generally together with a cross-linking promotor. Examples of
cross-linking promotors include functional vinyl compounds such as
divinylbenzene, polyethylene glycol dimethacrylate, triallyl
cyanurate, diallyl phthalate, 1,3-butadiene, 1,2-polybutadiene and
1,4-polybutadiene; quinone dioxime; and bisamide.
The process of this invention is described specifically. First, a
random copolymer of propylene and ethylene containing 1 to 10% by
weight ethylene and 99 to 90% by weight propylene (to be referred
to as a nuclear resin) is reduced to pellets having a size of 1 to
3 mm by, for example, extruding through an extruder. The pellets of
the nuclear resin are suspended in an aqueous medium containing a
dispersing agent. The dispersing agent may be, for example,
polyvinyl alcohol, methyl cellulose, calcium phosphate, magnesium
pyrophosphate, calcium carbonate, etc. The amount of the dispersing
agent employed is 0.01 to 5% by weight based on the amount of
water. Then, a vinyl aromatic monomer such as styrene monomer and a
polymerization catalyst are added to the resulting suspension
containing the nuclear resin particles dispersed therein. These
materials may be added all at one time, or gradually in small
portions. The vinyl aromatic monomer and the polymerization
catalyst may be added separately. Alternatively, the polymerization
catalyst may be first dissolved in, or mixed with, the vinyl
aromatic monomer, and the solution or mixture then added. The
polymerization catalyst may be used as a solution in a solvent
which does not hamper the polymerization reaction. Examples of
solvents that can be used for this purpose include toluene, benzene
and 1,2-dichloropropane.
In one embodiment of the present invention, the aqueous medium is
heated to a temperature at which the vinyl aromatic monomer can be
polymerized, and then the vinyl aromatic monomer and the
polymerization catalyst are added. Alternatively, these materials
are added at room temperature, and then the suspension is heated to
the polymerization temperature. When the cross-linking agent is
used in the process of this invention, it may be used by dissolving
in the vinyl aromatic monomer, or in the solvent for the
polymerization catalyst. When the vinyl aromatic monomer is used in
a relatively large amount, it is desirable to add the vinyl
aromatic monomer gradually in small portions to the suspension in
order to prevent the formation of a homopolymer of the vinyl
aromatic monomer.
The vinyl aromatic monomer added to the suspension penetrates into
the inside portion of the nuclear resin particles and is there
polymerized, or polymerized and cross-linked, in the nuclear resin
particles. As the result of this reaction, graft polymerization and
homopolymerization of the vinyl aromatic monomer take place
simultaneously. In this reaction, 20 to 70% by weight of the
nuclear resin and 30 to 80% by weight of the vinyl aromatic monomer
are used. When the amount of the vinyl aromatic monomer is smaller
than that above-specified, the expansion ratio of a resulting
foamed structure decreases, and a foamed structure of a high
expansion ratio cannot be obtained. On the other hand, when the
amount of the vinyl aromatic monomer is larger than the upper limit
specified, elasticity, thermal stability and oil resistance of the
resulting foamed product are deteriorated. Accordingly, the
proportions of the nuclear resin and the vinyl aromatic monomer
employed should be in the range of from 20 to 70% by weight,
preferably from 50 to 30% by weight, of the nuclear resin, and from
30 to 80% by weight, preferably from 50 to 70% by weight, of the
vinyl aromatic monomer.
The vinyl aromatic monomer added to the suspension is rapidly
absorbed into the inside portion of the nuclear resin particles,
and polymerized, or polymerized and cross-linked, within the
nuclear resin particles. Thus, the thermoplastic resin beads, in
accordance with this invention, are obtained. The resulting
thermoplastic resin particles consist of a random copolymer of
propylene and ethylene, a vinyl aromatic homopolymer and a graft
polymer of the random copolymer and vinyl aromatic monomer. Since
the above reaction provides thermoplastic resin beads containing
the graft random copolymer-vinyl aromatic monomer, phase separation
as seen in the case of simply mixing the random copolymer and the
vinyl aromatic homopolymer does not occur, and, thus, this graft
polymer exhibits a binder effect of increasing compatibility
between the random copolymer and the vinyl aromatic homopolymer.
For this reason, the random copolymer-vinyl aromatic graft
copolymer is required in an amount of at least 2%. If its
proportion is less than 2%, the binder effect is not sufficient,
and partial phase separation occurs in the resulting resin
beads.
The cross-linked polymer, if prepared by the process of this
invention, precipitates as an insoluble portion (gel) when
dissolved in hot toluene, xylene, etc. The amount of the reaction
product resulting from the grafting of the vinyl aromatic monomer
onto polypropylene is determined by the weight increase from the
initial amount of polypropylene used, which, in turn, is determined
from the residue of extraction with a 1:1 boiling mixture of
acetone and benzene. The presence of the gel or the graft reaction
product improves the retention of the blowing agent by the
resulting thermoplastic resin beads and the molding fusability of
the resin beads at the time of foaming.
In the process of this invention, for example, a blowing agent is
impregnated under pressure in the resulting thermoplastic resin
beads in an aqueous suspension. The suspending agent used in the
aqueous suspension is added in order to prevent bonding or
coalescing of the thermoplastic resin beads during impregnation of
the blowing agent. Examples of the suspending agent are organic
compounds such as partially saponified polyvinyl alcohol,
polyacrylic acid salt, polyvinyl pyrrolidone, carboxymethyl
cellulose, calcium stearate and ethylenebis stearamide, and,
sparingly, water-soluble fine powders of inorganic compounds such
as calcium pyrophosphate, calcium phosphate, calcium carbonate,
magnesium carbonate, magnesium phosphate, magnesium pyrophosphate
and magnesium oxide. When an inorganic compound is used as the
suspending agent in the process of this invention, it should be
desirably used together with a surface active agent such as sodium
dodecylbenzenesulfonate.
Easily volatilizable blowing agents are used in the process of this
invention. Examples of blowing agents include aliphatic
hydrocarbons such as propane, n-butane, i-butane, n-pentane,
i-pentane and n-hexane; cycloaliphatic hydrocarbons such as
cyclopentane and cyclohexane; and halogenated hydrocarbons such as
methyl chloride, ethyl chloride, dichlorodifluoromethane,
chlorodifluoromethane and trichlorofluoromethane. These blowing
agents are used in an amount of generally in the range of from 3 to
40% by weight based on the weight of the thermoplastic resin beads.
A small amount (for example, 1 to 5% by weight) of an organic
solvent such as toluene or xylene may be used together
therewith.
The impregnation of the blowing agent is performed, for example, by
suspending the thermoplastic resin beads in water containing the
suspending agent in an autoclave, heating the suspension, and
introducing the blowing agent under pressure. This procedure
affords expandable thermoplastic resin beads. Impregnation may also
be accomplished by, for example, dipping the thermoplastic resin
beads into a liquid blowing agent after the beads have been
prepared.
The glowing agent impregnated in the expandable thermoplastic resin
beads obtained by the process of this invention does not easily
escape from the beads, and the resin beads can be stored in a
stable condition over long periods of time. As a result, it is not
necessary, for example, as is the case with polyethylene-styrene
beads, to pre-foam the beads within 24 hours after preparation, or
to store them in a container under pressure. Therefore, resulting
expandable thermoplastic resin beads can be stored or transported
as prepared. For example, when the expandable resin particles, in
accordance with this invention, are prefoamed with steam after one
week storage at atmospheric pressure, foamed beads having a
sufficient expansion ratio can be obtained.
A foamed article having a high expansion factor can be prepared by
heating the expandable thermoplastic resin beads, in accordance
with disclosure of this invention, by a heating medium such as
steam. However, it has been found that, when a homopolymer of
propylene or a mixture of polypropylene and polyethylene is used as
the nuclear resin, it is difficult to obtain a foamed product
having a high expansion factor. According to the process of this
invention, a foamed article having an expansion ratio of 40 to 70
can be easily obtained. This is believed to be due to the following
reason. Since the nuclear resin used in the process of this
invention consists of a random copolymer of propylene and ethylene,
the degree of crystallinity of polypropylene decreases and its
melting point and flow initiating temperature are lowered to retard
crystallization. Hence, the dissipation of the blowing agent from
the beads at the time of foaming under heat can be prevented.
The expandable thermoplastic resin beads obtained by the process of
this invention can be formed into a foamed shaped article of a
desired configuration by pre-foaming the beads and foaming and
shaping them in a mold cavity. The resulting foamed shaped article
has superior thermal stability, chemical resistance (e.g., oil
resistance), and flexural strength due to the foamed polypropylene.
In particular, when the foamed article is used as an underlayer of
a roofing material to be subject to high temperatures, it is not
shrunk nor softened by heat, and, therefore, it finds extensive use
as a heat or sound insulating material or a cushioning
material.
Since according to the process of this invention, the blowing agent
is impregnated after the thermoplastic resin beads have been
prepared, it is not necessary to use a high pressure reactor for
polymerization and, optionally, cross-linking, and polymer beads
can be very easily obtained. While it has previously been thought
that cross-linking before the impregnation of a blowing agent
causes difficulty of impregnation of the blowing agent (Japanese
Patent Publication No. 32622/70), the process of this invention
makes it possible to obtain sufficiently expandable resin beads by
first performing polymerization and, optionally, cross-linking, and
thereafter impregnating the blowing agent. According to the process
of this invention, therefore, thermoplastic resin beads can be
obtained prior to the impregnation of the blowing agent by
polymerizing the vinyl aromatic monomer with the nuclear resin in
the presence of a polymerization catalyst and, optionally, a
cross-linking agent to induce graft polymerization or both graft
polymerization and cross-linking. These resin beads can be formed
into expandable thermoplastic resin beads in the manner described
hereinabove. These resin beads can also be used as a resin for
extrusion shaping. For example, it is possible to feed these beads
into an extruder, force a blowing agent into it, and extrude a
foamed sheet, plate or rod.
Furthermore, according to the process of this invention, it is
possible to add a fire retarding agent, a coloring agent, an
antistatic agent, etc.
The following Examples illustrate the present invention. Unless
otherwise specified, all parts and percentages are by weight.
EXAMPLES 1 TO 10
Forty(40) parts of a random copolymer of propylene and ethylene
containing 1% of ethylene which copolymer had been pelletized to a
diameter of 1 mm to 3 mm by an extruder was dispersed in a mixture
consisting of 150 parts of water, 0.2 part of magnesium
pyrophosphate prepared by the double decomposition-method and 0.02
part of sodium dodecylbenzenesulfonate. While maintaining the
dispersion at 85.degree. C. a solution of 0.3 part of benzoyl
peroxide and the amounts indicated in Table 1 of dicumyl peroxide
and a cross-linking promotor in 60 parts of styrene monomer was
added dropwise over the course of 7 hours. After the addition, the
reaction was conducted at 140.degree. C. for 4 hours. The reaction
product was cooled to obtain polymer beads. Then, a pressure
reactor was charged with 100 parts of the resulting polymer beads,
100 parts of water, 0.02 part of sodium dodecylbenzenesulfonate and
0.2 part of magnesium pyrophosphate, and 20 parts of butane was
introduced under pressure. The mixture was maintained at 80.degree.
C. for 6 hours. The mixture was then cooled to 30.degree. C.,
dehydrated and dried to obtain expandable thermoplastic resin
beads. The resin beads were maintained in an environment at
20.degree. C. in a closed vessel, and pre-foamed 3 to 4 days later.
These resin beads did not expand when contacted with hot water or
steam at 100.degree. C., but by heating them with steam or an oil
bath at 110.degree. to 150.degree. C., a foamed structure having
uniform closed cells was obtained.
The pre-expanded resin beads were placed into a mold having vapor
holes, and steam under a pressure of about 3.0 kg/cm.sup.2 (gauge
pressure) to 5.0 kg/cm.sup.2 was introduced for 30 to 100 seconds.
Then, the resulting foamed product was cooled with water, and
removed from the mold. The resulting foamed product was a good
quality molded product.
The amounts of the cross-linking agent and the cross-linking
promotor and the properties of the resulting foamed products are
shown in Table 1.
TABLE 1
__________________________________________________________________________
Amount of Cross-* Gel Polystyrene Dicumyl Linking Concen- Molding
Graft in Gel by Example Peroxide Promotor tration Expansion
Fusability Ratio IR Method No. (parts) (parts) (%) Ratio (%) (%)
(%)
__________________________________________________________________________
1 0 0 0 50 80 9.6 2 1 0 6.0 55 80 8.8 1.0 3 0.5 A 0.25 0.2 36 70
9.6 4 0.5 A 1.0 3.0 45 70 6.4 0.5 5 0.5 A 2.0 10 50 50 4.0 1.0 6
2.0 A 0.5 18 50 40 4.3 0.7 7 0.5 B 0.2 40 57 70 48.4 38.1 8 0.5 A
1.0 43 58 70 40.5 29.4 B 0.2 9 0.25 C 0.5 19 51 70 31.8 13.0 10
0.25 A 2.0 10 48 70 12.6 4.0
__________________________________________________________________________
"A" stands for 1,2polybutadiene "B" divinylbenzene "C" polyethylene
glycol dimethacrylate
The properties of the foamed products were measured by the
following methods.
Gel Concentration
Polymer beads obtained by polymerization were extracted with
boiling toluene for 16 hours, cooled, and then filtered. The
insoluble portion was dried under reduced pressure for 3 hours in
an oven at 120.degree. C. The percentage of the weight of the dried
insoluble portion based on the polymer beads was determined, and
made the gel concentration.
Expansion Ratio
This refers to the expansion ratio of expandable thermoplastic
resin beads to expanded beads which were prefoamed 4 days after
preparation. For example, in Example 1, expandable beads=1 and
expanded beads=50. Therefore, expansion ratio=1:50.
Molding Fusability
The molded product was broken by hand. When individual shapes of
foamed beads did not appear at all on the fractured surface, the
molding fusability was determined to be 100%. When the fractured
surface was entirely a surface showing individual shapes of foamed
beads, the molding fusability was determined to be 0%. Based on
this standard, the percentage of foamed particles at the fractured
surface was determined.
Graft Ratio
The sample was extracted with a 1:1 boiling mixture of acetone and
benzene for 6 hours, and the extraction residue was dried until its
weight became constant. The graft ratio was calculated in
accordance with the following equation. ##EQU1## W.sub.0 =the
weight of the sample W.sub.i =the weight of the extraction
residue
X=the proportion of polypropylene in the sample
The amount of polystyrene in the gel was determined by IR
analysis.
EXAMPLES 11 TO 17
The procedure of Examples 1 to 10 was repeated using the random
copolymer of propylene and ethylene including styrene with varying
contents of ethylene. The results are shown in Table 2. In these
Examples, dicumyl peroxide (0.2%) and 1,2-polybutadiene (1.0%) were
used.
TABLE 2 ______________________________________ Vapor Pressure
Content of during Example Ethylene Foaming Expansion No. (%) Melt
Index (kg/cm.sup.2) Ratio ______________________________________ 11
1.0 8 3.8 43 12 3 8 3.5 40 13 5 1.5 3.2 43 14 7 25 2.5 48 15 3 8
3.2 56 16 3 2.5 4.0 38 17 3 3.5 47
______________________________________
In Examples 15, 16 and 17, a mixture of 100 parts of the random
copolymer with 10, 15 and 5 parts, respectively, of low-density
polyethylene and 10, 10 and 5 parts, respectively, of EP rubber was
used.
EXAMPLES 18 TO 24 AND COMPARATIVE EXAMPLE 1
The procedure of Examples 1 to 10 was repeated except that the
random copolymer of propylene and ethylene containing 2% of
polyethylene was used in each of the amounts indicated in Table 3,
and the amount of styrene monomer was changed as shown in Table 3.
The results are shown in Table 3. In these examples, 2.0% of
1,2-polybutadiene and 1.0% of dicumyl peroxide were used.
For comparison, the above procedure was repeated except that the
proportion of the styrene monomer was decreased and the proportion
of the random copolymer was increased (Comparative Example 1). The
results are also shown in Table 3.
TABLE 3
__________________________________________________________________________
Vapor Gel Pressure Heat Random Styrene concen- during Molding
Dimensional Copolymer Monomer tration Foaming Expansion Fusability
Stability Example No. (%) (%) (%) (kg/cm.sup.2) Ratio (%) (%)
__________________________________________________________________________
18 70 30 25 4.3 16 20 -0.5 19 60 40 21 4.0 22 30 -1.0 20 50 50 19
3.5 33 60 -3.2 21 40 60 12 3.2 52 90 -4.1 22 30 70 5 2.5 60 90 -5.5
23 25 75 1.0 0.9 66 90 -7.0 24 20 80 1.0 0.5 64 90 -15.0
Comparative 75 25 30 4.5 14 0 Example 1
__________________________________________________________________________
In the above table, the heat dmensional stability denotes the
dimensional shrinkage of the sample based on the original dimension
compared with the sample after it was allowed to stand for 24 hours
in a hot air constant-temperature tank at 100.degree. C. Foamed
polystyrene itself has a heat dimensional stability of -23%.
The foamed product obtained in Comparative Example I had a low
expansion ratio, and very poor molding fusability.
While the invention has been described in detail and with reference
to specific embodiments thereof, it will be apparent to one skilled
in the art that various changes and modifications can be made
therein without departing from the spirit and scope thereof.
* * * * *